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DSLVDS1047-1048EVM: Signal extraction from the DSLVDS1047-1048EVM

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Replies: 2

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Part Number: DSLVDS1047-1048EVM

Hello -

from the evaluation module DSLVDS1047-1048EVM I want to extract the four differential LVDS signals available at the 8x2 output header J6 and pass them on to a board featuring DS90LT012AQ-Q1 LVDS receivers, which feature an integrated 100 ohm termination resistance.

On the evaluation module DSLVDS1047-1048EVM pins (1-3-…-15) of J6 are connected to GND, and the four LVDS signals are connected to pins (2-4-…-16). I intend extracting the LVDS signals from J6 using a ribbon cable. Accordingly wires 1-16 of the ribbon cable  are then assigned as 

GND  -  OUT4_N  -  GND  -  OUT4_P  -  GND  - … -  GND  -  OUT3_P  -  GND  -  OUT3_N

However, in this configuration, the differential line impedance between e.g  OUT4_P and OUT4_N on the ribbon cable is 2x the unbalanced impedance of the ribbon cable (see e.g. http://www.sigcon.com/Pubs/news/3_10.htm). For a standard 100 ohm ribbon cable that is then 200 ohm.

Is the mismatch between the differential line impedance (200 ohms here) and the 100 ohm system of the DS90LT012AQ acceptable? Is there a better method to extract the LVDS signals from the DSLVDS1047-1048EVM?

Feedback will be appreciated! Best wishes,

Rainer

  • Hello Rainer,

    The mismatch will likely to cause issues due to reflections, especially as the length of the cable increases. Unfortunately, I can't think of a clean way to carry the signals, short of a "custom cable" perhaps using individual wires. By the way don't forget to remove the termination resistors on the DSLVDS1047-1048EVM.

    Regards,
    Yaser
  • In reply to Yaser Ibrahim:

    Hi Yaser,

    many thanks for the feedback and the advice regarding the termination resistors at the output of driver ic.

    I have marked the issue as resolved.

    Best wishes, Rainer

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